Simplify the following expression: $r = \dfrac{5}{6a} + \dfrac{10}{7a}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $6a$ and $7a$ $\lcm(6a, 7a) = 42a$ $ r = \dfrac{7}{7} \cdot \dfrac{5}{6a} + \dfrac{6}{6} \cdot \dfrac{10}{7a} $ $r = \dfrac{35}{42a} + \dfrac{60}{42a}$ $r = \dfrac{35 +60}{42a}$ $r = \dfrac{95}{42a}$